TomTom One uses a Linear Technologies chip LTC3455 as a USB/charger power controller. See http://cds.linear.com/docs/Datasheet/3455fc.pdf. This chip is susceptible to high transient voltages that result from resonances created by parasitic inductances and capacitances of the USB/in-car charger cable . Good designs using this chip suggest that a 1 ohm resistance be put in the path of the cable to reduce the Q of the resonance and hence transient voltages. A 6V Zener diode D5 also serves to protect the chip from these transients.
If the Zener diode is blown it is most likely the the LTC3455 chip is gone as well. You can replace the chip which costs £5.00 (located in the shielded portion of the PCB). The recommended Zener Diodes for this chip are either the EDZ5.6B or EDZ6.2B manufactured by ROHM (http://www.rohm.com/products/databook/di/pdf/edz5.6b.pdf or http://www.rohm.com/products/databook/di/pdf/edz6.2b.pdf). These can be used to replace D5. The STMicroeletronics SM2T6V8A can also be used to replace D5 (http://www.st.com/stonline/products/literature/ds/8694/sm2t.pdf). All the Zeners cost a modest £0.22. I hope this is helpful.
Emmanuel Zyambo
Emmanuel Zyambo
October 2009